I've always put my original batten up such that there are 2 missing rows (1 full and 1 cut) at the bottom.
I don't understand how this works when there is a bath tub involved. Am I missing something?
Do you not put your first set of batons at 1 tile (or 1.5 tiles above the bath) and then follow this level around the room so the tiles meet. That's what I have done and I now need to tile below this level.